1. Field of the Invention
The present invention relates generally to burners for the combustion of fuel, and specifically to an improved high velocity dual fuel burner for optionally combusting gas or liquid fuel to fire a vertical shaft furnace for the continuous melting of metal pieces such as scrap copper.
2. Description of the Prior Art
In the prior art, there are many types of vertical furnace arrangements that have been used for melting various types of charge materials under a wide variety of different circumstances, such as the typical units disclosed in U.S. Pat. Nos. 2,203,163; 2,815,278; 2,886,304; 3,148,973; 3,199,977; 3,603,571; and, 3,958,919. U.S. Pat. Nos. 3,715,203; 3,788,623; and, 3,809,378 generally disclose specific types of furnace arrangements that are particularly useful in melting non-ferrous metals.
Modern industrial heating processes and especially metal melting furnaces require burners which have a number of preferred characteristics. Burners may generally be classified into three types, depending on the method of mixing the fuel and air.
The simplest arrangement, often called a throat-mix burner, consists of admitting the fuel and air into the combustion chamber through separate ports, usually adjacent to each other, and allowing the two to mix and burn in the furnace. This method of burning gives large, relatively slow-moving flames and has been widely used in firing open hearth steel furnaces.
A second type of mixing is found in the inspirator type of burner wheren the fuel is delivered to the burner under pressure and is discharged from a nozzle or jet in such a way that its momentum is used in mixing the fuel with indrawn air.
The third type of burner involves premixing all or part of the air with a gaseous fuel prior to delivery to the burner. With this arrangement the burner itself may be a relatively simple nozzle designed to deliver the combustible mixture without backfire or flame blowoff. A variety of arrangements are used for premixing and are well known in the art.
Within the prior art directed towards burners and their specific structural configurations, many varying types of burners have been designed to operate under a wide variety of particular applications and environments or for use in heating a material charge having various individual characteristics. Such burners include those as disclosed in U.S. Pat. Nos. 2,605,180; 3,701,517; 3,852,021; and 4,154,571.
Due to recent price increases and the widespread nonavailability of the cleaner gaseous fuels such as natural gas or propane or the like, it has become desirable to be able to burn various grades of fuel oils with such burners to provide the appropriate heating necessary for heating and melting a material charge within a furnace. Many attempts have been made at providing an effective liquid fuel burner such as those disclosed in U.S. Pat. Nos. 2,632,501; 2,697,910; 2,698,050; 2,711,214; 3,366,469; 2,205,983; 2,333,531; 2,632,300; 2,725,929; 3,042,105; 3,558,119; 3,749,548; 3,758,263; 3,777,983; 3,947,226; 3,980,415; 3,986,815; and, 4,025,282 and in U.S. Pat. application Ser. No. 921,039.
There are economic and logistic advantages and disadvantages in using either gas or liquid fuel systems. Natural gas fuel is normally less expensive than liquid fuel, but is available in sufficient supply, of at all, only seasonally. Gas fuel is also difficult to store at the site unless stored in liquid form such as liquified propane or butane or the like. Liquid fuel is usually more expensive but is also more available than gas fuel and easy to store as a reserve fuel supply. For these reasons, ability to optionally use gas and or liquid fuel would be highly advantageous, particularly in continuous industrial operations. This use of alternate fuels is possible under the prior art only by duplication of the separate types of burner systems including burners, manifolds and controls. However, duplication is expensive, inefficient and usually reduces the accurancy or ease of combustion control. The present invention provides the ability to optionally use gas and/or liquid fuel without system duplication by means of a novel burner design.